The present invention relates to a cathode ray tube, and particularly to a cathode ray tube wherein a contact spring for grounding thermoelectrons remaining on a phosphor layer to an external anode electrode and the coupling structure of the contact spring and cathode ray tube are improved.
Generally, as shown in FIG. 1, a cathode ray tube has an envelope formed by a funnel 2 and a panel 3. An electron gun 4 is inserted into a neck 2a provided at the rear end of funnel 2, and a graphite conductive layer 2b is formed on the inner surface of funnel 2. A phosphor layer 3a is formed on the inner surface of panel 3, and a plurality of stud pins 5 are installed inside of a skirt 3d at the periphery of phosphor layer 3a. Also, a shadow mask frame assembly 7' has a hook spring 6' coupled with stud pin 5 at each corner of the inner space of panel 3. A contact spring 9 having a circular contact portion 9a at its end in contact with graphite conductive layer 2b of funnel 2 is fixed on one side of a frame 8' of shadow mask frame assembly 7'.
In conventional cathode ray tube constructed as the above, electron beams emitted from electron gun 4 mounted on neck 2a of funnel 2 pass through the shadow mask, and then land on phosphor layer 3a, thereby forming a pixel. However, residual thermoelectrons remaining after illuminating phosphors on phosphor layer 3a impede the landing of succeeding thermoelectrons emitted from electron gun 4 on phosphor layer 3a. Thus, the residual thermoelectrons remaining after illuminating the phosphors on phosphor layer 3a are bypassed to the common ground of the circuit of the cathode ray tube.
In more detail, the residual thermoelectrons remaining after phosphor illumination are bypassed to the common ground of the circuit of the cathode ray tube via an aluminum deposited layer on the surface of a phosphor layer, a stud pin electrically connected to the aluminum deposited layer, a hook spring on which the stud pin is hooked, a frame to which the hook spring is fixed, a contact spring whose one end is fixed to the frame, a graphite conductive layer on the inner surface of a funnel which makes contact with the other end of the contact spring, and an anode electrically in contact with the graphite conductive layer, in sequence. Among the elements constituting the path for passing the thermoelectrons, since graphite conductive layer 3c which connects phosphor layer 3a, aluminum depositing layer 3b, and stud pin 5 as shown in FIG. 1 is a kind of coating film which is formed by a spray-on method or is brushed on by hand, the layer is easily separated from skirt 3d of panel 3 or the coating becomes ununiform which prevents the thermoelectrons from being smoothly passed. Such an inconsistent coating condition causes the thermoelectrons to not be completely passed under certain circumstances. Moreover, the graphite is frequently splashed onto the phosphor layer during its application, so that the manufactured product cannot be used due to the graphite contamination of the phosphor layer. In addition, contact spring 9 is fixed to frame 8' by an electric resistance welding process, in which foreign matter produced by sparks during welding remains on the shadow mask, thus clogging the beam passing holes of the shadow mask.